Stripping agent and method of use

ABSTRACT

A method of removing mercury adsorbed onto activated carbon is provided. The method includes treating an adsorbed mixture of metal cyanide complexes on a carbon substrate with an acidic solution of a stripping agent that is a weak acid. The method also eliminates inorganic scalants from the carbon substrate. In precious metal mining operations, the disclosed method reduces environmental emissions of mercury during the gold elution and carbon reactivation processes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/345,769, filed May 18, 2010; and U.S. Provisional Application No.61/417,133, filed Nov. 24, 2010, which are hereby incorporated byreference herein in their entirety.

GOVERNMENT LICENSE RIGHTS

This invention was made with government support under contractDE-FC26-02NT41607 awarded by the Department of Energy. The governmenthas certain rights in the invention.

TECHNICAL FIELD

The present disclosure relates to stripping agents and their uses,including removing mercury and inorganic sealants from activated carbonused in mining or metal recovery operations.

BACKGROUND

Precious metal production has evolved over the past several decades, andis based principally on the ability to dissolve precious metals using alixiviant, such as a basic aqueous cyanide solution, to form solublemetallocyanide complexes. Gold and silver are most notably recovered,but often the precious metal ores contain other metallic minerals, whichare also dissolved in the basic cyanide medium. The processes to recoverthe gold and silver cyanide complexes vary with the type of ore beingtreated, and the quantity of other metals in the solution. One of thesimplest (and most widespread) techniques is to adsorb themetallocyanide complexes onto activated carbon substrates, such as anactivated carbon derived from coconut shells. The carbon continues toadsorb the metallocyanide complexes until it reaches its ultimateloading, afterwards an elution process can be used to recover theprecious metals in a more concentrated solution. There are severalmethods by which the carbon can be applied, such as carbon in pulp(CIP), carbon in leach (CIL) and carbon in column (CIC) operations.While this technique is quite efficient and has been used widely in themining industry for over 50 years, it is not without its problems.

The most notable problem arises from the fact that ores often containother substances, such as metals or scalants, which can also be adsorbedwith the favored precious metal metallocyanide complexes. Specifically,cyano-complexes of mercury are also adsorbed on the activated carbontogether with the gold and silver cyanide complexes. This “contaminant”is a problem from many standpoints. First, the adsorbed mercury cyanidecomplexes occupy space on the activated carbon, thereby reducing thespace available for adsorbing the favored precious metals. Secondly, themercury generally follows the precious metals in subsequent processes,requiring additional and expensive processing steps to remove andrecover the mercury separately from the gold and silver. Thirdly,mercury is a strictly regulated “toxic substance” that must be handledwith expensive processes to minimize or eliminate its release to theenvironment.

Elution (stripping) of the gold and silver cyanide complexes from theactivated carbon for recovery of these precious metals may beaccomplished by treating the activated carbon with a stripping agent.Generally, the adsorbed mixture of precious metal cyanide complexesadsorbed on the activated carbon is treated with a sodium cyanide/sodiumhydroxide stripping agent solution at elevated temperatures. Whenmercury cyanide complexes are also adsorbed, some of the mercury will beeluted with the gold and silver. However, a significant percentage ofthe mercury will remain affixed to the carbon after elution, reducingthe effectiveness of the carbon as it is recycled to process moresolution.

As stated above, metallocyanide complexes are not the only substancesthat are adsorbed on the carbon. In fact, inorganic and/or organicfouling is a recurring problem in gold and silver production facilities.Inorganic scalants include various forms of lime scale (CaCO₃, CaSO₄)and adsorb and blind large areas of the carbon. These inorganic scalantscan remain even after the precious metals are eluted from the carbon,which is typically accomplished using a basic aqueous cyanide solutioneluent. However, an acid rinse with a strong acid, such as hydrochloricacid, may be used to dissolve the inorganic scalants prior to elutingthe precious metal complexes from the carbon.

Oils, greases and other volatile organic compounds are also readilyadsorbed by activated carbon. But these volatile organic compounds maybe removed from the carbon after the precious metals have been strippedby heating the carbon to elevated temperatures using “in-house”regeneration kilns prior to the carbon being returned to process moresolution. However, any mercury that is not desorbed from the activatedcarbon can also become volatilized from the carbon in thehigh-temperature regeneration (or reactivation) process, and may bepotentially emitted to the environment.

Accordingly, a need exists for new methods for desorbing mercury and/orinorganic scalants from an activated carbon, such as when used in miningor metal recovery operations.

SUMMARY OF THE INVENTION

Certain aspects of the present disclosure are described in the appendedclaims. There are additional features and advantages of the subjectmatter described herein. They will become apparent as this specificationproceeds. In this regard, it is to be understood that the claims serveas a brief summary of varying aspects of the subject matter describedherein. The various features described in the claims and below forvarious embodiments may be used in combination or separately. Anyparticular embodiment need not provide all features noted above, norsolve all problems or address all issues noted above.

According to an embodiment of the invention, a method of removingmercury from an adsorbed mixture comprising mercury and gold that isadsorbed on a carbon substrate is provided. The method includesdesorbing mercury from the carbon substrate by contacting the adsorbedmixture with an acidic aqueous solution comprising a stripping agentthat is a weak acid.

According to another embodiment of the invention, a method of removingan inorganic scalant from an adsorbed mixture comprising the inorganicscalant, mercury, and gold that is adsorbed on an activated carbon usedin a precious metal recovery process is provided. The method includesdesorbing the inorganic scalant from the carbon substrate by contactingthe adsorbed mixture with an acidic aqueous solution comprising astripping agent that is a weak acid.

According to another embodiment of the invention, a method of reducingmercury emissions in precious metal mining operations is provided. Themethod includes washing an adsorbed mixture comprising mercury and goldthat is adsorbed on an activated carbon substrate, with an acidicaqueous solution comprising a stripping agent that is a weak acid,wherein at least a portion of a first amount of mercury is desorbed fromthe activated carbon substrate. The method further includes removing atleast a portion of the gold from the activated carbon substrate, andregenerating the activated carbon substrate by heating, wherein a secondamount of mercury remaining on the activated carbon substrate isvolatilized from the activated carbon substrate, the second amount ofmercury is less than the first amount of mercury.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the invention and,together with a general description of the invention given above, andthe detailed description of the embodiments given below, serve toexplain the principles of the invention.

FIG. 1 is a graph of the percentage of mercury stripped and Hg/Austripping ratio versus number of stripping steps according to anembodiment of the present disclosure; and

FIG. 2 is a graph of the amount of mercury that remained adsorbed onactivated carbon (percent) versus elution temperature using sodiumhydroxide and sodium cyanide over twenty-four hours of elution.

DETAILED DESCRIPTION OF EMBODIMENTS

Unless otherwise explained, all technical and scientific terms usedherein have the same meaning as commonly understood by one of ordinaryskill in the art to which this disclosure belongs. In case of conflict,the present specification, including explanations of terms, willcontrol. The singular terms “a,” “an,” and “the” include pluralreferents unless context clearly indicates otherwise. Similarly, theword “or” is intended to include “and” unless the context clearlyindicates otherwise. The term “comprising” means “including;” hence,“comprising A or B” means including A or B, as well as A and B together.

According to the present disclosure, methods of removing mercury from anactivated carbon substrate are provided. The process also has the addedbenefit of eliminating calcium salts and other inorganic scalants thatcan accumulate on activated carbon used to recover precious metalcyanide complexes from leach solutions. These methods, which upon theirapplication to precious metal mining, operations, advantageously alsoprovides separating mercury from precious metals, such as gold, and alsoreduces atmospheric emissions of mercury, as discussed below. Theprocedures disclosed can be substituted into the processing streamwithout adding unit operations or unit processing steps to the currentphysical plant of a mining operation.

The starting materials for the methods described herein can includeactivated carbon, such as for use in precious metal mining operations toconcentrate and recover precious metal cyanide complexes from leachsolutions. Carbon substrates suitable for use with the described methodsinclude those activated carbons generally used in the precious metalmining industry, and can include those carbon substrates having highporosity and superficial area of more than 1000 m²/g. In one example,the pores may have diameters of about 10-20 Angstroms. One commonly usedactivated carbon substrate is available from Carbon Activated Corp. ofCompton, Calif. (item number 004-C activated carbon, coconut shell 6×12mesh).

The ores suitable for the methods described herein are not particularlylimited to any specific type of precious metal-containing ore. However,gold ores found in the state of Nevada in the United States of Americaare exemplary of ores that also contain significant amounts of mercury.

According to embodiments of the invention, an acidic aqueous solutionthat includes a stripping agent of a weak acid is used to desorb mercuryfrom the adsorbed mixture of the metal cyanide complexes on the carbonsubstrate. As used herein, a weak acid is an acid that dissociatesincompletely and therefore has a higher pKa than a strong acid, such ashydrochloric acid, which effectively releases substantially all of itsacidic proton(s) when dissolved in water, i.e., completely dissociates.Examples of weak acids include some inorganic acids, such as phosphoricacid, and organic acids, such as carboxylic acids. Suitable organicacids include formic acid (HCOOH), acetic acid (CH₃COOH), proprionicacid (CH₃CH₂COOH), tannic acid, oxalic acid, citric acid, and the like.Exemplary carboxylic acids include mono acids, such as formic acid,acetic acid, and proprionic acid.

The concentration of the stripping agent in the acidic aqueous solutionmay range from greater than 0% to about 30 percent by volume. Forexample, the stripping agent concentration may be about 5%, 10%, 15%,20%, 25%, or 30% by volume. According to various embodiments, thestripping agent concentration may be a dilute concentration, such asfrom about 0.5% by volume to about 10% by volume, from about 2% byvolume to about 8% by volume, from about 3% by volume to about 7% byvolume, from about 4% to about 6% by volume, or from about 4.5% to about5.5% by volume.

In addition to water, the acidic aqueous solutions may also include oneor more co-solvents such as alcohols. For example, methanol, ethanol andthe like may be used as a co-solvent.

The acidic aqueous solutions, which include the stripping agent, and theadsorbed mixture may be intermixed under a variety of contactingtemperatures and conditions. According to embodiments of the invention,the contacting temperature may range from about 40° C. to about 120° C.to affect about 75% desorption of the available mercury from theactivated carbon substrate over a 24 hour period, as shown in FIG. 2.According to certain embodiments, the contacting temperature may be fromabout 50° C. to about 110° C., from about 60° C. to about 100° C., fromabout 70° C. to about 100° C., or from about 80° C. to about 90° C.

The acidic aqueous solutions and the adsorbed mixture of metal cyanidecomplexes and activated carbon substrate may be contacted under batch orflow conditions. In batch operations, the combined mixture of the acidicaqueous solutions and the adsorbed mixture may be mixed or agitated byany known manner, such as stirring or shaking. In flow operations,various parameters, such as flow rate, column dimensions, flowconfiguration, pressure, and the like may be optimized to affect thedesired desorption results.

According to embodiments of the invention, the acidic aqueous solutionwith its stripping agent selectively desorbs and removes mercury fromthe activated carbon substrate, while substantially leaving the preciousmetals such as gold adsorbed on the activated carbon substrate. In oneexample, the acidic aqueous solution with its stripping agent removedabout 35.4 wt % of the total adsorbed mercury on the adsorbed mixture,while only removing about 0.124% of the total adsorbed gold from theadsorbed mixture, which provides a selectivity of (35.4)/(0.124) or 285Hg:Au stripped ratio. According to one embodiment of the invention, theHg:Au stripped ratio is about 100 or more, about 200 or more, about 300or more, about 400 or more, about 500 or more, or about 600 or more. Inanother example, the Hg:Au stripped ratio can range from about 100 toabout 700.

Another advantage of the disclosed methods is the reduction of inorganicscalants, such as calcium carbonate and/or calcium sulfate, that canalso be adsorbed onto the activated carbon substrate. The acidic aqueoussolution with its stripping agent can dissolve these foulants andthereby obviate or substantially reduce the amount of acid washinggenerally used in many reactivation procedures, as discussed below.

After the desired amount of mercury has been desorbed and removed fromthe adsorbed mixture, the adsorbed precious metals may be removed by anysuitable method, e.g., elution with 2.5 wt % NaCN and 2.5 wt % NaOH at130° C.

After the precious metals have been sufficiently desorbed and removedfrom the carbon substrate of the adsorbed mixture, the carbon generallyneeds to be reactivated, e.g., by heating at elevated temperatures in areducing atmosphere. Therefore, the elimination or substantial reductionof mercury content remaining on the carbon substrate minimizes theamount of mercury that will be volatilized during the kilning process.As such, the methods disclosed herein allow for the reduction in mercuryemissions to the environment during precious metal mining operations.

Although methods and materials similar or equivalent to those describedherein can be used in the practice or testing of the present disclosure,suitable methods and materials are described herein. The disclosedmaterials, methods, and examples are illustrative only and not intendedto be limiting.

General Experimental Details

Mercury Analysis: An Atomic Absorption/Mercury Cold Vapor Technique wasused. To obtain metallurgical balances, the amount of mercury containedin the carbon was first established. Oxidants used were KMnO₄ and K₂S₂O₈and aqua regia was used as lixiviant. The technique developed is asfollows: after filtration and water rinsing and drying, 1, 2 or 3 gramsof carbon was digested in 10 ml of aqua regia at 95° C. for 2 minutes;2.5 ml of 5% Na₂S₂O₈ was added and heated at 95° C. for 30 minutes; andthen 5 ml of 5% KMnO₄ was added and heated at 95° C. for 30 minutes. Thesupernatant was poured off and analyzed using a SpectraAA-200 AtomicAbsorption Spectrophotometer, manufactured by Varian. This procedurerepresented one stage of digestion. After five stages, approximately 90%of the mercury was desorbed.

Gold Analysis: Gold-bearing solution was diluted with 5% HNO₃ to aselected volume so that its gold concentration was within the range of0-2 ppm, and then analyzed with the SpectraAA-200 spectrophotometer.

Evaluation of acetic acid as a stripping agent: The addition of aceticacid as a stripping agent selectively desorbs mercury cyanide fromactivated carbon leaving gold cyanide adsorbed on the carbon. Resultsfrom a method according to the present disclosure are provided in Table1 and FIG. 1.

TABLE 1 Effect of concentration of acetic acid. Conditions: 2.0 g carbonloaded with 4.3 mg Au/g C and 4.5 mg Hg/g C; 37.5 ml water plus aceticacid, stripping - 1 hour at 60° C. Conc. of Acetic Acid Stripped (%)Stripped (Vol %) Hg Au Hg/Au Ratio 5 30.9 0.046 672 10 42.7 0.063 678 2043.6 0.10 436 30 48.6 0.16 304

As shown in Table 1, using a 10 vol % of acetic acid stripping agent at60° C. provided that 42.7% of the adsorbed mercury was stripped from thecarbon after one hour of elution, while only 0.063% of the gold wasdesorbed, which gave a 678 Hg:Au stripped ratio.

Mercury stripping was also conducted with five 1-hour stripping stages(total of five hours). Stripping conditions were: 2.0 g carbon loadedwith 4.3 mg Au/g C and 4.5 mg Hg/g C. The solution volume was 37.5 ml,the temperature was 80° C., and the solution was 10 vol % acetic acid.Results are shown in FIG. 1. The stripping stages were conducted withfresh 10 vol % acetic acid in each case.

Under these conditions 51.8% of the mercury was stripped in one stage ofstripping. After five stages of stripping, 85.1% of the mercury waseluted from the activated carbon.

Methanol/Ethanol

Methanol and ethanol can be used as eluants for selective stripping ofmercury cyanide from Au(CN)₂ ⁻ when both cyano complexes are adsorbed onactivated carbon. Results from using this method are shown in Tables 2and 3. Conditions for the stripping were: 1.00 g carbon, loaded with 4.7mg Au and 4.2 mg Hg; solvent volume 15 ml; these substances were placedin a 250-ml Erlenmeyer flask with a rubber stopper seal, and shaken for5 seconds every 10 minutes for 1 hour.

TABLE 2 Stripping of mercury cyanide and Au(CN)₂ ⁻ from carbon (100%alcohol). Temperature 23° C. 52° C. Desorbed Metal Hg (%) Au (%) Hg (%)Au (%) Methanol 41.4 39.6 69.6 38.7 Ethanol 15.7 16.3 24.8 21.7

TABLE 3 Stripping of mercury cyanide and Au(CN)₂ ⁻ from carbon withvarious concentrations of methanol at 52° C. Methanol/H₂O 100/0 50/5025/75 0/100 Desorbed Metal Hg Au Hg Au Hg Au Hg Au Desorbed Amount 69.639.1 31.7 28.3 18.8 17.7 2.0 0.04 (%)

These results indicated that methanol was superior to ethanol as astripping agent. However, selective separation of mercury cyanidespecies and Au(CN)₂ ⁻ was not observed with either of these reagents at23° C. And while increased desorption of the metal cyano complexes wasobserved at higher temperatures, only modest selectivity was observed.

Effect of Various Acids

Stripping efficiency of mercury cyanide was evaluated in the presence ofvarious acids in the presence and absence of methanol. The conditionsused were 2.00 g carbon loaded with Au4.3 mg/g and Hg4.5 mg/g; strippingsolution (methanol/H₂O= 25/75 vol %); volume=30 ml; shaken for 1 hour at60±1° C. in a water bath. The addition of the acids into the totalvolume of 30 ml is given in Table 4.

TABLE 4 Mercury cyanide and Au(CN)₂ ⁻ desorption with various acids inthe presence of 25 vol % methanol. Dose Stripped % Stripped Acid (ml org) pH Hg Au Ratio (Hg/Au) Temp. HNO₃ 0.36 0.74 18.7 0.22 85 60° C. HCl0.09 1.92 4.1 0.06 68 50° C. H₃PO₄ 0.36 1.17 35.4 0.124 285 60° C.Perchloric 0.36 1.1 40.8 0.20 204 60° C. Formic 1.5 2.2 36.7 0.107 34360° C. Acetic 1.5 3.3 34.4 0.104 303 60° C. 3.0 3.2 41.0 0.13 315 60° C.Tannic 1.5 g 3.7 39.2 0.28 140 60° C. Oxalic 1.5 g 1.1 35.2 0.20 176 60°C. Citric 1.5 g 2.4 24.3 0.10 243 60° C.

Of these acids, nitric and hydrochloric acids were somewhat lesseffective in selectively stripping mercury cyanide from gold cyanide inthe presence of 25 vol % methanol.

Propionic acid was also evaluated as a stripping agent. Table 5 shows Hgdesorption data using propionic acid. 1.00 gm carbon was loaded with 1.0mg Hg/g C. Stripping with various total solution volumes of 10 vol %propionic acid for 6.0 hrs at 80° C.

TABLE 5 Hg desorption data using propionic acid. Solution volume, Hgdesorbed, Carbon, g ml mg Desorbed, % 1.0 10 0.607 60.7 1.0 25 0.84084.0 1.0 80 0.840 84.0

Propionic acid functions as an effective stripping agent for mercurycyanide from activated carbon. Under the experimental conditionsstudied, up to 84 percent of the adsorbed Hg desorbed from the carbonafter stripping with 25 ml of 10 vol % propionic acid for 6 hours.

Effect of Temperature

The effects of temperature and time on mercury and gold elution fromcarbon with sodium cyanide and sodium hydroxide were evaluated indetail. In these methods, 3.33 g of carbon was loaded with 4.1 mg Hg/g Cand 4.7 mg Au/g C. As shown in FIG. 2, optimal elution temperatureranges from 80° C. to 90° C. in which only about 2 wt % of the initialmercury was retained on the carbon. At the conventional elutiontemperature of 135° C., about 25% of the initial mercury remains on thecarbon.

Without intending to be limited by theory, the optimal temperature rangemight be explained on the following basis. From room temperature toabout 90° C., the kinetics of desorption increases with increasingtemperature. Above about 100° C., the mercury cyanide complexes becomeunstable, and mercuric hydroxide forms. Conditions used for this exampleof the method were: carbon 3.3 g; elution solution: 500 ml;(NaCN)=(NaOH)=2.5 wt %; Au loading 4.7 mg/g; Hg loading 4.1 mg/g.

Effective and selective stripping of mercury cyanide from Au(CN)₂ ⁻ canbe accomplished using acetic acid when both species are adsorbed onactivated carbon. In some cases, 95% or greater desorption of themercury from the carbon can be accomplished while leaving virtually allof the gold cyanide on the carbon.

Acid Washing

In typical gold processing operations, activated carbons loaded(adsorbed) with gold cyanide, are washed with dilute solutions ofmineral acids, such as HCl or HNO₃, in order to remove certain inorganicscalants, such as CaCO₃. It was unexpectedly found that washing theloaded carbon with a dilute solution of an organic acid, such as aceticacid, removes inorganic scalants, and also removes mercury cyanidecomplexes from the substrate (carbon), without substantially removingvaluable precious metal cyanide complexes, such as cyanide compounds ofgold or silver, from the substrate. After washing has been carried outto a desired degree, the carbon is moved to the stripping operation.

It is to be understood that the above discussion provides a detaileddescription of various embodiments. The above descriptions will enablethose skilled in the art to make many departures from the particularexamples described above to provide apparatuses constructed inaccordance with the present disclosure. The embodiments areillustrative, and not intended to limit the scope of the presentdisclosure. The scope of the present disclosure is rather to bedetermined by the scope of the claims as issued and equivalents thereto.

What is claimed is:
 1. A method of removing mercury from an adsorbedmixture comprising mercury and gold that is adsorbed on a carbonsubstrate, the method comprising: desorbing mercury from the carbonsubstrate by contacting the adsorbed mixture with an acidic aqueoussolution comprising a stripping agent that is a weak acid.
 2. The methodof claim 1, wherein prior to desorbing mercury from the carbonsubstrate, the method further comprises: adsorbing mercury and gold onthe carbon substrate to form the adsorbed mixture, which includesmercury and gold.
 3. The method of claim 1, wherein the weak acidcomprises phosphoric acid.
 4. The method of claim 1, wherein the weakacid comprises an organic acid.
 5. The method of claim 1, wherein theweak acid comprises a carboxylic acid.
 6. The method of claim 5, whereinthe carboxylic acid is a mono acid.
 7. The method of claim 6, whereinthe mono acid is selected from the group consisting of formic acid,acetic acid, and propionic acid.
 8. The method of claim 1, wherein theacidic solution further comprises an alcohol.
 9. The method of claim 1,wherein desorbing mercury from the carbon substrate comprises contactingthe adsorbed mixture with the acidic aqueous solution at a temperaturefrom about 40° C. to about 120° C.
 10. The method of claim 1, whereindesorbing mercury from the carbon substrate comprises contacting theadsorbed mixture with the acidic aqueous solution at a temperature fromabout 60° C. to about 100° C.
 11. The method of claim 1, whereindesorbing mercury from the carbon substrate comprises contacting theadsorbed mixture with the acidic aqueous solution at a temperature fromabout 80° C. to about 90° C.
 12. The method of claim 1, wherein the weakacid is present in a concentration greater than 0% and less than about30% by volume of the acidic aqueous solution.
 13. The method of claim 1,wherein the weak acid is present in a concentration from about 5% toabout 20% by volume of the acidic aqueous solution.
 14. The method ofclaim 1, wherein the weak acid is present in a concentration from about5% to about 10% by volume of the acidic aqueous solution.
 15. A methodof removing an inorganic scalant from an adsorbed mixture comprising theinorganic scalant, mercury, and gold that is adsorbed on an activatedcarbon used in a precious metal recovery processes, the methodcomprising: desorbing the inorganic scalant from the carbon substrate bycontacting the adsorbed mixture with an acidic aqueous solutioncomprising a stripping agent that is a weak acid.
 16. The method ofclaim 15, wherein the weak acid comprises phosphoric acid.
 17. Themethod of claim 15, wherein the weak acid comprises an organic acid. 18.The method of claim 15, wherein the weak acid comprises a carboxylicacid.
 19. The method of claim 18, wherein the carboxylic acid is a monoacid.
 20. The method of claim 19, wherein the mono acid is selected fromthe group consisting of formic acid, acetic acid, and propionic acid.21. The method of claim 15, wherein the acidic solution furthercomprises an alcohol.
 22. The method of claim 15, wherein desorbing theinorganic scalant from the carbon substrate comprises contacting theadsorbed mixture with the acidic aqueous solution at a temperature fromabout 40° C. to about 120° C.
 23. The method of claim 15, whereindesorbing the inorganic sealant from the carbon substrate comprisescontacting the adsorbed mixture with the acidic aqueous solution at atemperature from about 60° C. to about 100° C.
 24. The method of claim15, wherein desorbing the inorganic sealant from the carbon substratecomprises contacting the adsorbed mixture with the acidic aqueoussolution at a temperature from about 80° C. to about 90° C.
 25. Themethod of claim 15, wherein the weak acid is present in a concentrationgreater than 0% and less than about 30% by volume of the acidic aqueoussolution.
 26. The method of claim 15, wherein the weak acid is presentin a concentration from about 5% to about 20% by volume of the acidicaqueous solution.
 27. The method of claim 15, wherein the weak acid ispresent in a concentration from about 5% to about 10% by volume of theacidic aqueous solution.
 28. The method of claim 15, wherein theinorganic sealant includes a calcium precipitate.
 29. The method ofclaim 28, wherein the calcium precipitate is calcium carbonate.
 30. Themethod of claim 28, wherein the calcium precipitate is calcium sulfate.31. The method of claim 15, wherein desorbing the inorganic sealant fromthe carbon substrate by contacting the adsorbed mixture with the acidicaqueous solution further includes desorbing mercury from the carbonsubstrate.
 32. A method of reducing mercury emissions in precious metalmining operations, comprising: washing an adsorbed mixture comprisingmercury and gold that is adsorbed on an activated carbon substrate withan acidic aqueous solution comprising a stripping agent that is a weakacid, wherein at least a portion of a first amount of mercury isdesorbed from the activated carbon substrate; removing at least aportion of the gold from the activated carbon substrate; andregenerating the activated carbon substrate by heating, wherein a secondamount of mercury remaining on the activated carbon substrate isvolatilized from the activated carbon substrate, the second amount ofmercury is less than the first amount of mercury.
 33. The method ofclaim 32, wherein the weak acid comprises phosphoric acid.
 34. Themethod of claim 32, wherein the weak acid comprises an organic acid. 35.The method of claim 32, wherein the weak acid comprises a carboxylicacid.
 36. The method of claim 35, wherein the carboxylic acid is a monoacid.
 37. The method of claim 36, wherein the mono acid is selected fromthe group consisting of formic acid, acetic acid, and propionic acid.38. The method of claim 32, wherein the acidic aqueous solution furthercomprises an alcohol.
 39. The method of claim 32, wherein the mercury isdesorbed from the carbon substrate by washing the adsorbed mixture withthe acidic aqueous solution at a temperature from about 40° C. to about120° C.
 40. The method of claim 32, wherein the mercury is desorbed fromthe carbon substrate by washing the adsorbed mixture with the acidicaqueous solution at a temperature from about 60° C. to about 100° C. 41.The method of claim 32, wherein the mercury is desorbed from the carbonsubstrate by washing the adsorbed mixture with the acidic aqueoussolution at a temperature from about 80° C. to about 90° C.
 42. Themethod of claim 32, wherein the weak acid is present in a concentrationgreater than 0% and less than about 30% by volume of the acidic aqueoussolution.
 43. The method of claim 32, wherein the weak acid is presentin a concentration from about 5% to about 20% by volume of the acidicaqueous solution.
 44. The method of claim 32, wherein the weak acid ispresent in a concentration from about 5% to about 10% by volume of theacidic aqueous solution.